A stent is a medical device provided for propping open an obstructed passage within the body, such as a blocked ureter. In general, ureteral blockage is a medical condition requiring treatment. A ureteral blockage can occur for a number of reasons, including the passage of a kidney stone and/or other material into the ureter where it becomes entrapped. Also, a tumor growing against the outer wall of the ureter can force compression or constriction of the ureter. A tumor on the internal ureteral wall can also cause blockage of the ureter. Ureteral stents are often used to correct such problems. A ureteral stent may be placed inside the ureter on a temporary basis to allow proper drainage of fluids from the kidney to the bladder. A ureteral stent usually comprises a straight length of hollow tubing with each end having a hook or a curl or other configuration for preventing migration or expulsion of the stent from its placed position within the ureter. One end of a typical ureteral stent is placed in the kidney and the other end is placed in the bladder. The end positioned in the kidney is typically configured to retain the stent within the renal pelvis and to prevent the downward migration of the stent into the ureter. The bladder end of the stent is typically configured to prevent upward migration of the stent towards the kidney.
FIG. 1 is a conceptual background drawing showing a portion of the human urinary tract. Referring to FIG. 1, in a human urinary tract 100, the ureters 102 and 104 transport urine from the kidneys 106 and 108 to the bladder 110. The trigone region of the bladder 112 is located between the urethral opening 114 and the two ureteral orifices 116 and 118. The pain associated with an in-dwelling ureteral stent is attributable in-part to contact between the stent and the bladder mucosa 120 in the trigone region 112. The trigone region 112 is believed to be particularly innervated and sensitive to the presence of any foreign bodies such as the bladder end of a ureteral stent. The intramural tunnel regions 122 and 124 of the ureters 102 and 104, respectively, act like valves, shutting off to prevent back flow of urine from the bladder 112 to the kidneys 106 and 108. The intramural tunnel regions 122 and 124 are also believed to be particularly innervated and sensitive to the presence of any foreign bodies. In addition, further discomfort due to in-dwelling stents can be caused by flank pain due to urine shooting from the bladder 110 back up the ureters 102 and 104 intra-luminally via the stent, and/or extra-luminally around the stent.